WO 97/21457, which is incorporated herein by reference, discloses a liquid drug delivery device having a base member defining a skin-contacting surface for application to the skin of a subject. A columnar cartridge serving as a reservoir for the drug is connected to the base member such that in use the longitudinal axis of the cartridge is disposed substantially parallel to the skin-contacting surface. A delivery needle communicates in use with the interior of the cartridge and is adapted to penetrate the skin of the subject, and there is provided means for expelling a drug out of the interior of the cartridge and through the skin of the subject via the delivery needle.
It has been found that adapting conventional cartridges (such as cartridges for pen-type insulin injectors, or other drug cartridges well known in the art) so as to enable an expelling means to expel the drug therefrom, and so as to enable communication with a delivery needle forming part of such a device, increases the costs of the cartridge considerably, and this in turn adds to the cost of the overall device and hence its attractiveness to consumers. The main reason for this is that conventional drug cartridges are relatively inexpensive, but redesigning such a component and changing the manufacturing process, or individually modifying such components drives costs up considerably.
Nevertheless, in technical terms, the devices of WO 97/21457 have undoubted advantages over the prior art due to the fact that the disposition of the cartridge parallel to the skin enables the device to be applied to the skin and worn unobtrusively during drug delivery. Both application of the device and delivery of the drug can be accomplished in a single step requiring little or no manual dexterity.
A further problem associated with the devices of WO 97/21457 is in relation to the delivery needle which effectively extends at right angles to the axis of the cartridge. This may be accomplished by using a conduit arrangement leading from the cartridge to a conventional needle, or by means of a right-angled needle which extends from an end of the cartridge co-axially with the axis of the cartridge and then bends through a right angle to penetrate the skin. The latter arrangement is preferred since it reduces the number of parts and the complexity of the device. However, it may prove difficult to bend a needle while maintaining sterility (which is of course essential), since the sterility of the needle is assured by a protective sheath which extends the entire length of the needle and which may be damaged in the bending process.
For devices which employ a needle to penetrate the skin there is a danger that after use the device may accidentally infect the patient or others if not properly disposed of. Our WO 95/13838 discloses an intradermal device of this type having a displaceable cover which is moved between a first position in which the needle is retracted before use and a second position in which the needle is exposed during use. Removal of the device from the skin causes the cover to return to the first position in which the needle is again retracted before disposal.
The present invention aims to decrease the possibilities that the needle could become exposed by accident before or after use for example by a child playing with the device if not properly disposed of. Clearly given the risks associated with infectious diseases, particularly those carried by blood, any possibility of accidental infection must be minimised to the utmost and preferably eliminated entirely.
Some of the features of devices according to the invention which address these problems are set out below, and further advantages will become apparent from the following description.
In devices of the present invention, a conventional syringe barrel is mounted relative to a base member defining a skin-contacting surface, with the longitudinal axis of the needle substantially parallel to the skin-contacting surface in use.